1. Field
The following description relates to a bias circuit providing different bias voltages depending on a power mode, and a power amplifier having the same.
2. Description of Related Art
In general, a main purpose of a power amplifier is to supply power to a load. The power amplifier is generally referred to as a last stage amplifier because it is generally positioned in a final stage of amplifying circuits.
It is important for the power amplifier to have a small degree of distortion and to efficiently supply the power to the load. Therefore, typically, a power transistor is used as an amplifying element of the power amplifier.
In light of the explosive growth of wireless communications technology, a large number of people are enabled to wirelessly transmit and receive information through portable devices, such as mobile devices, regardless of time and place. However, because the use of wireless communications by such large number of people has increased, various services have been required. To satisfy user demand for such services, portable terminals have been provided with increased functionality, causing a problem in that an amount of time that the portable terminals may continuously operate has significantly reduced.
The reduction in continuous operation of the portable terminals and, therefore, a reduction of maximum talk time for a user of the portable terminal are mainly caused by device power consumption and are caused because battery capacity of the portable terminal is limited. In a case in which battery capacity is increased, a volume of the portable terminal increases leading to user-desired thinness and lightness not to being satisfied. As a result, there is a need for efficient power usage.
The power amplifier described above may also be adopted for use in a portable terminal to be utilized for wireless communications, and may be used to amplify a level of a transmitted or received signal. Therefore, in order to realize efficient power usage in the portable terminal, efficient power usage is also required in the power amplifier. Therefore, the power amplifier performs a selective operation in a high power mode and in a low power mode.
The above-mentioned power amplifier is supplied with a bias voltage to perform an amplifying operation. In general, because the power amplifier is supplied with the same bias voltage at the time of operations in the high power mode and in the low power mode, there is a problem in that the power may be inefficiently used.
In order to solve the above-mentioned problem, a method of supplying different bias voltages depending on the power mode is needed. In existing methods, depending on the power mode, different bias circuits need to be individually provided, resulting in an increased a circuit area, which consequentially causes a further problem in that the volume of the portable terminal is increased.